The invention relates to a flow machine for a fluid.
Radial sealing gaps are often provided in flow machines between the rotor and the stator parts, which are normally narrowly designed in order to keep the flow losses small. If the rotor part and the stator part touch in certain operating conditions, such as on starting up of the flow machine, this can lead to wear of the stator parts and/or of the rotor and to an undesired widening of the sealing gap. If the fluid contains solid materials, this can likewise lead to wear in the narrow sealing gaps.
In order to counteract an undesired widening of the sealing gap, protective layers and/or self-supporting wear rings of wear-resistant materials are used for this reason in the sealing gaps. Wear rings of this kind do have high resistance to wear, however they can only be manufactured in simple forms due to their resistance to wear. A further disadvantage is the small thermal expansion coefficient in comparison to other materials and the low elasticity of wear rings of this kind. During thermal start-up transients, such as those occurring during the pumping of hot fluids, for example, the rotor wheel heats up due to the throughflow and the smaller mass faster than the wear ring inserted in a stator part. In this connection, with steep transients, the narrow sealing gap can shrink below a permissible size or can even be by-passed, which can lead to a premature widening of the sealing gap or even to damaging of the flow machine.